Gas turbine engines may be used to power various types of vehicles and systems, such as air or land-based vehicles. In typical gas turbine engines, compressed air generated by axial and/or radial compressors is mixed with fuel and burned, and the expanding hot combustion gases are directed along a flowpath and through a turbine nozzle having stationary turbine vanes. The gas flow deflects off of the vanes and impinges upon turbine blades of a turbine rotor. A rotatable turbine disk or wheel, from which the turbine blades extend, spins at high speeds to produce power. Gas turbine engines used in aircraft use the power to draw more air into the engine and to pass high velocity combustion gas out of the gas turbine aft end to produce a forward thrust. Other gas turbine engines may use the power to turn a propeller or an electrical generator.
Typically, the stationary turbine vanes of the turbine nozzle extend between an inner ring and an outer ring. The inner and outer rings define a portion of the flowpath along which the combustion gases travel. In some cases, to simplify manufacture of the turbine nozzle, the inner and/or outer rings are initially formed as segments, and the segments are subsequently assembled together to form a full ring or bonded together. In other cases, the vanes are bi-cast with the inner and outer rings, so that the rings and the vanes form a single, unitary structure.
Although the aforementioned turbine nozzles operate adequately under most circumstances, they may be improved. In particular, in configurations in which the inner and outer rings of the turbine nozzle comprise numerous segments, gas leakage may occur at interfaces between adjacent segments. As a result, a chargeable cooling flow may be unintentionally added to the gas flowing through the turbine nozzle, which may cause the turbine engine to increase fuel consumption. In some instances, leakage between the adjacent segments may result in decreased combustor cooling. Though bi-cast inner and outer rings reduce leakage of turbine nozzles, they may be relatively difficult and/or time consuming to manufacture. Additionally, coatings, such as thermal barrier layers, may be relatively difficult to apply to bi-cast turbine nozzles. In particular, because of limitations with deposition apparatus and processes for forming thermal barrier layers, formation of the thermal barrier layers on the stationary vanes may be a relatively complex process. In addition, bi-cast or brazed full ring turbine nozzles suffer from thermo-mechanical fatigue (TMF) due to the thermo-mechanical stresses that develop between the vanes and the inner ring and between the vanes and the outer ring.
Accordingly, it is desirable to have an improved turbine nozzle that has minimal gas leakage and is simpler and less expensive to manufacture than conventional turbine nozzles. In addition, it is desirable for the improved turbine nozzle to be capable of being retrofitted into existing engines. Furthermore, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description of the inventive subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the inventive subject matter.